Measuring apparatus are known which utilize the paramagnetic characteristic of oxygen to measure the oxygen content of gases. Since the paramagnetic effect is small, the difference is always measured between the signal generated by the measured gas and the signal which is generated by a means for displacing the measured gas. The means displacing the measured gas is a displacing body in dumbbell devices and in induction devices which moves in a magnetic field. Such devices are disclosed, for example, in U.S. Pat. Nos. 4,763,509 and 4,808,922. The invention relates to a material for producing such a displacing body.
In dumbbell devices, the displacing body is produced as a dumbbell-shaped body comprising two small hollow glass balls which are interconnected by a glass fiber. This production process is complex and the displacing body is mechanically very sensitive. The dumbbell shape of the displacing body further compels a specific configuration of the pole shoes of the magnet which generates the magnetic field required for measuring the oxygen content of the measuring gas. This configuration is disadvantageous since the magnetic field generated thereby is weak.
The displacing body for induction devices has the form of a rotating cuvette which has one or more chambers for the gas to be investigated. In order that the cuvette itself does not generate any spurious signal, it is necessary that the same quantity of cuvette material always be disposed in the magnetic field during rotation of the cuvette when the magnetic susceptibility of the cuvette material is non-vanishing. This requires very tight manufacturing tolerances and requires a specific configuration of the cuvette. Furthermore, the cuvette material must have a high degree of homogeneity.
The following requirements are imposed on an optimal displacing body:
(a) the displacing body must have an adequate mechanical strength and a volume which is as constant as possible and which is not dependent in an unpredictable manner from gas pressure, temperature, humidity or chemical influences; PA1 (b) the magnetic susceptibility of the displacing body must be as constant as possible; PA1 (c) the displacing body should be economically producible in a form which allows for an optimal formation of the magnetic field; PA1 (d) the displacing body should be as light as possible since the shock sensitivity of the measuring device is thereby reduced and the response time is improved; and, PA1 (e) the magnetic susceptibility of the displacing body should be close to zero since it will then not be necessary to impose requirements on the consistency of the magnetic field needed for the measurement which are too high.